1. Field of the Invention
The present invention relates to a film winding apparatus of a camera. More precisely, it relates to a film winding apparatus in which a film feed can be precisely and reliably detected by a photoelectric element.
2. Description of Related Art
To detect the feed position of a film, upon loading the film, the winding film, or rewinding the film, in a film winding apparatus of a conventional camera, an electric switch is mechanically actuated by a sprocket, which is engaged with perforations of the film. It is difficult, however, to ensure reliability of such a mechanically actuated electric switch. To this end, particularly in recent electronic cameras, it is known to provide a photoelectric element, such as a photoreflector, for counting the number of perforations of the film to detect the feed position thereof.
The photoelectric element can provide for a more reliable operation of the apparatus, but has a drawback in that the output value of the photoreflector fluctuates depending on the particular film that is used. The output of the photoreflector may also fluctuate due to irregular characteristics of the photoreflector. In such a case, for example, it is necessary to compare the output signal of the photoelectric element with a predetermined threshold value (corresponding to the presence or absence of a perforation) and count the times that the output signal intersects the threshold value in order to count the number of perforations. However, if there is a large variation in the output level of the photoelectric element, the output level might not reach the threshold value, resulting in an incorrect number of counted perforations.